50: Pulmonary Circulation

Question 1

What is the total blood volume in pulmonary vasculature?

Answer 1

600 ml supine falls by 20%

on standing

Question 2

What happens to blood volume during forced inspiration?

Answer 2

allows an increase to ~1

liter by reducing intrathoracic pressure – opening vessels up

Question 3

What happens to blood volume during forced expiration?

Answer 3

reduces volume to ~300

ml by raising intrathoracic pressure

Question 4

What is the blood volume in pulmonary capillaries at

any 1 instant?

Answer 4

100 mL

Question 5

What happens to blood volume during heavy exercise?

Answer 5

increase from 100 to 150 mL

Question 6

Increased cross sectional area (and higher resident volume) helps to slow blood down where?

Answer 6

Capillaries

Question 7

Systemic arteries/arterioles

Answer 7

thick and have a lot of smooth muscle

divert blood flow to places with max requirements

Question 8

Pulmonary arteries

Answer 8

little smooth muscle and thin walls (very compliant)

Question 9

Pulmonary capillary

Answer 9

walls are very very thin

Question 10

Why are Pulmonary

Pressures so Low?

Answer 10

high pressures would cause blood to drain into lungs

Question 11

Threshold for edema?

Answer 11

25 mm Hg

Hydrostatic pressure is high
enough to push fluid out of
blood into alveoli

Question 12

How much of the cardiac output does the lung receive?

Answer 12

receives 100% of CO

5L at rest
20L during exercise

Question 13

How much pressure drives flow in the systemic vasculature?

Answer 13

100 mm Hg

100 mm Hg/ 5L = 20 units

Question 14

How much pressure drives flow in the pulmonary circuit?

Answer 14

7 mm Hg

7 mm Hg/ 5L = 1.4 units

Question 15

Pulmonary Vascular Resistance

Answer 15

decreases as cardiac output increases

more blood pumped out, pulmonary arterial pressure increases, pulmonary vascular resistance decreases

Question 16

Pulmonary Arterial Pressure

Answer 16

minimal increase during exercise to avoid edema

5 mm Hg increase in
pressure results in 4x the flow b/c of increase CO

Question 17

Recruitment

Answer 17

use of already available cross sectional area

Question 18

Distention

Answer 18

vasodilation can open up new cross sectional area to further

augment total cross sectional area

Question 19

Extra-alveolar vessels

Answer 19

larger and
have a web of interlinking
alveolar vessels between them in
parallel

Question 20

What is the alveolar vessels response to change in lung volume?

Answer 20

Alveolar vessels in walls of alveoli

vessels pulled closed as alveoli expand

resistance increases as the lung inflates

like stretching rubber band

Question 21

What is the extra-alveolar vessels response to change in lung volume?

Answer 21

sensitive to
radial traction (high
transpulmonary pressures) and pull open as alveoli expand

resistance decreases as the lung inflates

Question 22

Forces promoting fluid filtration

Answer 22

↑capillary hydrostatic pressure
↓colloid oncotic pressure
↑surface tension
↓lymphatic drainage
↑ capillary permeability

Question 23

Forces promoting fluid absorption

Answer 23

↑ colloid oncotic pressure
↑ air pressure
↓ capillary hydrostatic pressure

Question 24

Regional hypoxia

Answer 24

promotes vasoconstriction

less blood to that area of the lung

Question 25

Global hypoxia

Answer 25

all capillary beds and lungs vasoconstrict b/c low oxygen

can cause high altitude pulmonary edema

Question 26

Nifedipine

Answer 26

calcium channel blocker

prevents high altitude pulmonary edema

Question 27

Where does most ventilation of the lung go?

Answer 27

Base of lung b/c of gravity

Question 28

Where does least ventilation of the lung go?

Answer 28

Apex of lung

Question 29

Which side of heart is low pressure pump?

Answer 29

Right heart

Question 30

Low or No Ventilation

Answer 30

leads to shunt

venous blood has gas exchange at alveoli and comes back to left heart deoxygenated

Question 31

Pulmonary Capillary Wedge Pressure (PCWP)

Answer 31

cardiac catheterization to read left atrial pressures

Used to determine degree of congestion in
pulmonary circuit

Heart failure & pulmonary congestion : increased PCWP

Question 32

Increasing Shunt

Answer 32

administering oxygen does not change blood oxygen levels

leads to hypoxemia (low oxygen in blood)

Question 33

Lung Zoning

Answer 33

Zone 3: arterial and venous pressure must exceed alveolar pressure so no compression along length of vessel